1. Related Technical Fields
Related technical fields include navigation devices, methods, and programs that perform map matching for navigation.
2. Related Art
On-vehicle navigation devices that find a travel route to a destination and guide the vehicle are widely used. This type of navigation device estimates the current position of the vehicle, and uses a map matching process to identify the road on which the vehicle is currently traveling, in addition to displaying the vehicle's current position on a map and providing travel guidance.
FIGS. 9A to 9C show an outline of the map matching process. As shown in FIG. 9A for example, if the vehicle position estimated from the traveling distance and heading is an estimated position P1 with respect to an actual vehicle position R, then the current position of the vehicle can be matched to a road on the map by matching the current position to either one of candidate points A1, B1 on roads A, B in the vicinity of the estimated position P1. Matching to the candidate points A1, B1 may be determined based on their distances from the estimated position P1 or a difference between the heading in the advancing direction and the road headings, for example.
However, the matching process may falsely match the estimated position P1 after passing a branch point shown in FIG. 9A to the candidate point A1. In such case, as shown in FIG. 9B, if subsequent travel on the road is nearly straight, the matching process may continue to match an estimated position P2 at the next matching point to the falsely matched road A. Then, as FIG. 9C shows, at an estimated position P3 where the direction of the actually traveled road B changes considerably, the false matching is corrected when a match is made to a candidate point B3 on the road B and the current position is thus corrected to the candidate point B3 on the correct road.
Matching to the correct road may thus be delayed, particularly in the case of a false match after traveling a road that branches at a narrow angle. Hence, due to the high probability of a false match after a junction, a threshold is conventionally set as a predetermined distance traveled from the junction and map matching delayed until the threshold is traveled.
Art according to Japanese Patent Application Publication No. JP-A-2005-114632 describes map matching that takes into account the road widths at branch points and the amount of space between roads. In the case of a method that prevents false matching by using a distance traveled from the junction, however, a match is not necessarily made to the correct road after passing the threshold.